Duty cycle

Duty cycle answers the same underlying question — what fraction of the time is the arc actually burning — at two different scales, and conflating them produces a number that means nothing to whoever reads it next.

At the equipment level, duty cycle is a thermal rating: the manufacturer specifies the maximum share of a fixed reference period, most commonly ten minutes, that the power source can deliver its rated output current before internal protection has to let it cool. Run above the rated current and the duty cycle the source can sustain drops; run below it and the source can sustain a higher duty cycle than its nameplate figure. This rating is a property of the machine, fixed at the point of manufacture, and it bounds what the process can physically sustain regardless of how the cell is scheduled.

At the production level, duty cycle — sometimes called the operating factor — describes how the cell is actually used: the share of a shift, or of any longer period, that the arc is striking rather than the cell sitting idle for fixture loading, part changeover, torch maintenance or waiting on an upstream station. This number has nothing to do with the power source’s thermal limit; a cell can run at 20% arc-on time while its power source is individually rated for a much higher duty cycle, simply because most of the shift is spent on non-welding tasks. It is this operating-factor sense that a deposition rate calculation for a shift, rather than for a single continuous pass, needs as a separate input from wire feed speed: feed speed sets deposition rate while the arc is burning, and duty cycle sets how much of the shift the arc burns for.

The two meanings are related in one practical direction: robotic and automated cells generally run far higher production duty cycles than manual welding, which is exactly why deposition rate and cell throughput scale differently between the two even at an identical wire feed speed and travel speed. Reporting a duty cycle number without saying which of the two definitions it uses is the single most common way the term gets misread between an equipment datasheet and a production report.